If you get crashed with a message containing that string, you may notice that iMessage just keeps rebooting. That's because that string is still hiding in your history. We have to get rid of it. First you have to make your User Library visible:

Open a terminal window

Enter "sudo chflags nohidden ~/Library/"

Press Return

Enter your password when prompted.

Once you've done that, the most sure-fire fix is to delete your entire iMessages history:

Quit iMessage

Hit Command+Shift+G and enter

Enter "~/Library/Messages/" in the Go To Folder window that appears

Take all the "chat.db" and "chat.db-*" files and put them in the trash

Empty the trash

Restart iMessage

In the meantime, just hope your prankster friends aren't savvy enough to know they can crash your iMessages with just a couple of characters. Either that, or get them before they get you. [Thanks Steve T-S and Manfred Scheiner!]

Update: We removed any instances of the actual text string from the post and headline because it was crashing folks' Safaris. SORRY GUYS.